I forgot to say that this blog is also accessible for IPv6 users. Unfortunately I couldn't get my registrar to enter an ipv6-glue record yet. So DNS will still need to be performed over v4.

More IPv6-related posts will come, especially as I notice that lots of applications are not even aware v6 exists...Filling in bug reports as we speak/read/write.

Normally, to configure IPv6 (and v4) forwarding on a Linux system you should edit the /etc/sysctl.conf file and change the lines like this:

# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1

# Uncomment the next line to enable packet forwarding for IPv6
net.ipv6.ip_forward=1

This way your kernel will load the forwarding parameters on next reboot.
To activate the feature without rebooting do:

# echo 1 > /proc/sys/net/ipv4/conf/all/forwarding 
# echo 1 > /proc/sys/net/ipv6/conf/all/forwarding

But suddenly you get the following error with ipv6:

# echo 1 > /proc/sys/net/ipv6/conf/all/forwarding 
-bash: /proc/sys/net/ipv6/conf/all/forwarding: Permission denied

In my setup I run Linux as guest in OpenVZ. It seemed my OpenVZ wasn't fully configured to allow IPv6. (I run it trough Proxmox). To enable full IPv6 support I edited the /etc/vz/vz.conf file and set IPV6="yes".

This still didn't solve the problem, even after rebooting the server completely.
Currently I couldn't find a way to get it working correctly, so I created a fully virtualized machine with bridged networking.
I hope to find a way to get ipv6 forwarding working correctly in OpenVZ soon, a post with the solution will follow then.

Don't start debugging your radvd if your Virtual Guest doesn't work correctly with IPv6. All the VMware products have a problem with IPv6 route advertisements over a briged network connection going over a wireless link.
Your virtual machine will get an IPv6, but will not get the IPv6 gateway.

To disable IPv6 in Ubuntu add the following line blacklist ipv6 in the /etc/modprobe.d/blacklist file. If you don't want to reboot you can try to remove the IPv6 kernel module with the sudo rmmod command. But that failed with me as the module was in use.

VMWare filed this as bug #26078, communities forum link

To force Firefox to use IPv4 DNS resolution instead of IPv6 go in your about:config tab and change the value network.dns.disableIPv6 to true

The little story: Last week-end I started the migration of my private network from IPv4 to IPv6. As I'm temporarily back at my parents place I do have to maintain a certain internet-availability.
An IPv4 to IPv6 migration is not that easy, especially when your ISP is still speaking IPv4. This means I have to tunnel all my IPv6 traffic to a tunneling service.

All this means quite some complex configurations as I want to do all the intelligence on the Linksys WRT54GL v1.1. This device is a little limited in memory and is giving me some issues with the DD-WRT firmware and the extra software I need for this. Well, it just takes more time than expected. So having a mixed (working) IPv4 and (not working) IPv6 internet gave me an unexpected problem: Firefox will use IPv6 name resolution if available. If your IPv6 packets don't reach further than your router, you just can't access all the sites anymore...that's why forcing IPv4 in Firefox can be useful.

If you're busy with networking or security the following paper is certainly a good lecture. Understanding the protocols can lead to finding possible attacks. Reading about possible attacks can sometimes motivate people to learn more about the protocols...

Exploiting Tomorrow's Internet Today: Penetration testing with IPv6

This paper illustrates how IPv6-enabled systems with link-local and auto-configured addresses can be compromised using existing security tools. While most of the techniques described can apply to "real" IPv6 networks, the focus of this paper is to target IPv6-enabled systems on the local network.

This paper is written by H D Moore, he's the main author behind Metasploit and was invited at FOSDEM in 2007.